Method for producing insoluble sulfur

ABSTRACT

A PROCESS FOR PRODUCING INSOLUBLE SULFUR IS DISCLOSED AND INCLUDES THE STEPS OF MELTING AND HEATING SULFUR TO A TEMPERATURE OF FROM 400 TO 800* F. AND THEREAFTER QUICKLY QUENCHING THE MOLTEN SULFUR WITHIN AN AQUEOUS SOLUTION CONTAINING HYDROGEN PEROXIDE.

Sept 5, 1972 M. J. BLOCK METHOD FOR PRODUCING INSOLUBLE SULFUR Filed NOV. 12, 1971 M o R 5 4 5 a fr m 5 a u 4 .4 w M w. 5 Mo,... 4 W y i M M w f 2 x z a r a a A wm 2 a a 5 5 l! f2 y ,4 EAW/#2 RK o N Evi 7 M 6 f/ 4 ac w. 4 4 /2 10m 2/ M EH HM aM* Y Wa B @5%. ,Wa/ ...w |.a -J -w of. l5 -4 W m Q37 M 4 2 E -2 .0J y a A -f w M W w United States Patent 3,689,227 METHOD FOR PRODUCING INSOLUBLE SULFUR Michael J. Block, Fullerton, Calif., assignor t Union Oil Company of California, Los Angeles, Calif. Filed Nov. 12, 1971, Ser. No. 198,129 Int. Cl. C01b 17/12; C01d 9/00; B01d 11/02 U.S. Cl. 23-293 10 Claims ABSTRACT OF THE DISCLOSURE A process for producing insoluble sulfur is disclosed and includes the steps of melting and heating sulfur to a temperature of from 400 to 800 P. and thereafter quickly quenching the molten sulfur within an aqueous solution containing hydrogen peroxide.

DESCRIPTION OF THE INVENTION This invention relates to the manufacture of insoluble sulfur and more particularly to an improved process for making insoluble sulfur which is stable at ambient conditions.

BACKGROUND OF THE INVENTION Several methods have been proposed for the preparation of insoluble sulfur, i.e., polymeric sulfur stable at ambient conditions and characterized by being insoluble in carbon disulfide. These methods commonly involve quenching the molten or vaporous sulfur within a hydrocarbon or chlorinated hydrocarbon bath. These methods, while quite satisfactory for the preparation of insoluble sulfur, are burdened by economic and procedural disadvantages. For example, the process requires the employment of 'bulk quantities of expensive quenching solutions. It also requires stringent safeguard procedures in instances where toxic chlorinated hydrocarbons are employed. The process must also be air tight so that oxygen from the air does not enter the system and form explosive mixtures.

In another commonly practiced method, the disadvantages of the hydrocarbon systems are avoided by quenching the molten sulfur in an aqueous solution of nitric or hydrochloric acid and an electrolyte salt. This method is disclosed in U.S. Pat. No. 2,513,524 to Alvin Schallis. Although the process is relatively trouble-free, the product sulfur is adulterated with foreign material from electrolytic acid bath. Thus, upon quenching the molten sulfur, a small amount of the acid and electrolyte salt is occluded within the solidified sulfur particles or absorbed onto the particle surface. This foreign matter is carried along with the sulfur particles, and, depending upon the ultimate use of the insoluble sulfur, may pose a serious contamination problem.

Other proposed methods, such as, the quenching of molten sulfur in water, aqueous acids, alkalines, etc.; have not been as successful as the aforesaid processes in producing insoluble sulfur which is stable in air at ambient conditions. In general, these latter processes result in the production of less stable polymeric sulfur and require the immediate addition of stabilizers, such as olefins, etc. to inhibit the sulfur reversion to the soluble form.

Accordingly, it is an object of this invention to pro- Ivide a process for producing insoluble sulfur.

It is another object of this invention to provide a process for producing relatively pure insoluble sulfur.

It is an additional object of this invention to provide a process for economically producing insoluble sulfur which is stable in air at ambient conditions.

Other and related objects of this invention will become apparent from the following description and ac- Patented Sept. 5, 1972 lCe companying drawing, of which: IFIG. 1 displays an exemplary process flow diagram for the process; and FIG. 2 is a plot of the reversion stability of insoluble sulfur prepared by different processes.

The aforementioned objects and their attendant advantages can be realized by quenching molten polymeric sulfur within an aqueous solution containing hydrogen peroxide. The presence of the hydrogen peroxide within the quenching bath aids in retarding the reversion of the insoluble sulfur to the soluble form, and also stabilizes the sulfur after its removal from the bath over prolonged periods not heretofore obtained within the aid of stabilizing additives.

In accordance with the practice of this invention, the sulfur is heated in lthe molten state at -a temperature of 400 to 832 F. and preferably from 500 to 700 F. At these temperatures the molten sulfur immediately transforms into the polymeric form, e.g., mu sulfur. The molten polymeric sulfur is then quickly quenched by direct contact with an aqueous hydrogen peroxide bath held at a temperature between 35 and 100 F. and more preferably between about 40 and 75 F. When sulfur temperatures higher than 832 F. are employed, the sulfur begins to exert a substantial vapor pressure and pressurized systems must be employed. Alternatively, when I'temperatures lower than 400 F. are employed, the molten sulfur has a high viscosity and pressure drops throughout the system become burdensome.

The amount of aqueous peroxide bath which must be present during the quenching step must be sufiicient so as to maintain the temperature below F.`Although the amount of quenching medium employed is not critical to this invention, provided the temperatures are within the desired ranges, the aqueous peroxide bath is generally maintained from 20 to 5000 pounds per pound of sulfur, based on the amount of sulfur present in the quenching medium at any time. More preferably, the amount of quenching medium is maintained from 50 to 1000 pounds per pound of sulfur. y.

The amount of hydrogen peroxide which may be ernployed to stabilize the polymeric sulfur can vary from 0.1 to 30 weight percent of the aqueous medium, however, concentrations above 10 weight percent are not recommended since highly concentrated peroxide solutions become unstable and hazardous. Preferably, the amount of hydrogen peroxide is maintained between about 0.5 and 5 weight percent and more preferably between 1 and 3 weight percent.

The sulfur is preferably injected into the quenching medium as small droplets or fibers to increase the surface area exposed to the peroxide solution. I have found that the greater the exposed droplet or fiber surface area, the greater the product stability. The droplet or fiber diameter is preferably below 0.25 inch and more preferably between 0.066 (10 mesh) and 0.0015 inch (400 mesh), and more preferably between about l0.011 inch (50 mesh) and 0.0025 inch (250 mesh). These droplets or fibers can be obtained by injecting the molten polymeric sulfur through a nozzle or small orifice.

The molten sulfur droplets or fibers leaving the nozzle or orifice should contact the quenching medium as soon as possible, and preferably within 0.1 second. If longer times are employed, some reversion on the particle surface may occur, as well as undesired coalesence of the particles. In one embodiment, this time is rendered diminimus by placing the nozzle or orifice immediately on the surface of the aqueous cooling medium so that quenching occurs immediately upon being discharged from the nozzle or orifice.

It is additionally preferred to agitate the aqueous medium during quenching so as to quickly circulate the cool fluid around the solidifying sulfur particles. The agitator employed is not critical to the invention and can comprise any axial or radial ow impeller mixer or, alternatively, an in situ injector mixer.

Whenever a dispersion of sulfur in water occurs within a circulating system as a result of sulfur quenching, cavitation of pumps as well as quick agglomeration of the particles within the aqueous medium occurs. These difficulties can be conveniently avoided, or at least diminished, by the addition to the quenching medium of a watersoluble surfactant. The surfactant reduces the interfacial tension of the water and allows the surface of the sulfur particles to become water-wet. The surfactant must also be inert to the sulfur particles at the operating conditions.

The water soluble surfactants which may be added to the quenching medium can be of the nonionic, cationic, amphoteric or anionic type. Examples of water-soluble anionic surface active agents are: alkyl benzene sulfonates, such as sodium dodecyl or tridecyl-benzene sulfonate: alkyl diphenyl sulfonates, such as sodium butyl diphenyl sulfonate; alkyl naphthalene sulfonates, such as sodium diisopropyl naphthalene sulfonate, ammonium diamyl naphthalene sulfonate, sodium mono-nonyl naphthalene sulfonate, sodium isopropyl or isobutyl naphthalene sulfonate and sodium dinonyl naphthalene sulfonate; soaps, such as potassium palmitate, triethanolamine oleate, morpholine stearate, sodium laurate and ammonium myristate; sulfated aliphatic alcohols, such as sodium hexadecyl sulfate, sodium oleyl sulfate, triethanolamine dodecyl sulfate, sodium 3,9-diethyl -tridecanol sulfate, sodium 2-methyl-7-ethyl-4-undecanol sulfate and sodium Z-ethyl-l-hexanol sulfate; sulfated and sulfonated fatty oils, acids or esters, such as the sodium salt of sulfonated castor oil, the sodium salt of sulfated red oil, the sodium salt of sulfonated butyl oleate and the sodium salt of sulfonated isopropyl oleate; alkyl sulfophthalates, such as sodium hexadecyl sulfophthalate; sulfated amides, such as sulfated hydroxy-ethyl a luramide and sulfated hydroxyisopropyl palmitamide; sodium salt of lauryl sulfo acetate; sodium salt of dioctyl sulfo-succinate; sodium salt of oleylmethyl tauride; sodium salt of sulfonated dodecyl benzoate, and the like. Examples of water-soluble cationic surface active agents are: salts of primary, secondary and tertiary amines, such as oleyl amine acetate, dodecyl amine acetate, dioctyl amine lactate, stearoyldiethanolamine acetate and dilauroyl triethylene-tetramine diacetate; and quaternary salts, such as lauryl pyridinium bromide, octadecyl ethyl morpholinium chloride, lauryloxyethyl di-(hydroxy ethyl) ethyl ammonium ethyl sulfate, oleyloxy-ethyl trimethyl ammonium ethyl sulfate, dodecyl trimethyl ammonium chloride, and the like.

Examples of water-soluble nonionic surface active agents include: partial esters of polyhydric alcohols, such as nonethylene glycol monolaurate and tricosaethylene glycol monolaurate; condensation products of alkyl phenols with ethylene oxide such as the reaction product of isooctyl phenol with 12 ethylene oxide units; condensation products of alkyl thiophenols with to 15 ethylene oxide units; condensation products of higher fatty alcohols with ethylene oxide such as the reaction products of oleyl alcohol with 10 to 15 or more ethylene oxide units; ethylene oxide adducts of monoesters of hexahydric alcohols and inner ethers thereof, such as sorbitan monolaurate, sorbitol monooleate and mannitan monopalmitate, and the like.

The quantity of surface active agent which may be employed to improve the dispersibility of the sulfur droplets in the quenching medium as well as to prevent pump cavitation varies depending upon the specific operating conditions employed, type of surfactant selected, etc. Generally, however, the amount of surface active agent ranges from 0.001 to 1.0 weight percent preferably from 0.01 to 0.1 Weight percent. Addition of substantially greater amounts of the agent serves no added function, but, rather, may be detrimental by posing a contamination problem.

Upon quenching the polymeric sulfur, the solidied particles are separated from the aqueous peroxide solution and the aqueous medium recycled to the quenching zone. By recycling the filtered solution in this manner, the addition of water and hydrogen peroxide may be minimized and the operating costs substantially reduced.

The recovered sulfur particles contain major amounts (40-60 percent) of reverted or soluble sulfur which must be separated from the polymeric or insoluble form in order to realize a commercial product. The soluble sulfur may be separated from the insoluble form by conventional solvent extraction processes. In a typical process, the crude sulfur particles are contacted with a solvent in a liquid-solid contactor for a period sufficient to extract at least percent and preferably at least 90 percent of the soluble sulfur from the crude particles. Exemplary solvents which may be employed include, carbon disulfide, ethylene dichloride, methylene dichloride, benzene, toluene, xylene, etc. Carbon disulfide is preferred because of its greater solubilizing ability. The extracted sulfur particles are then ltered from the liquid solvent, dried and packaged.

A particularly preferred embodiment of this invention is illustrated by a process ow diagram displayed in FIG. l. As shown in the figure, sulfur is conveyed by a suitable conduct 4 to a melting chamber 2. Heat is supplied to the chamber through heater 6 to melt the sulfur and increase its temperature to approximately 300 F. The molten sulfur leaves chamber 2 through line 8 and enters a second heating chamber 10. The molten sulfur within chamber 10 is heated by heater 12 to a temperature of approximately 50G-700 F. and sufficient to polymerize the molten sulfur. The molten polymerized sulfur is then injected through lines 16 and nozzles 18 into quenching chamber 14 containing an aqueous hydrogen peroxide solution. The aqueous quenching medium is agitated with a radial flow impeller mixer 20 so as to provide moderate to violent mixing of the sulfur and aqueous peroxide solution.

A portion of the quenching medium containing dispersed particles of solidified polymeric sulfur is removed from chamber 14 through line 22 and discharged into rotary filter 24. The aqueous solution is separated from the sulfur particles `and returned to chamber 14 through pump 26 and return line 28. Since the molten sulfur is being cooled, the quenching medium must be similarly cooled in order to maintain its temperature between 60- 70 F. Accordingly, heat exchanger 30 is connected within the return line 28 to cool the recycle solution. Make up water and surfactant are introduced into the aqueous quenching medium through lines 32 and 34 respectively which connect to return line 28.

The filtered sulfur is conveyed through conveying line 36 to the top of a counter-current extraction column 38. A carbon disulfide solvent is introduced into the bottom of the column and travels upwardly within the column counter-current to the particulate sulfur. The solvent extracts the soluble sulfur from the particles without dissolving any of the polymeric or insoluble sulfur.

The sulfur laden solvent is recovered at the top of the extraction column through line 40 and introduced into a flash chamber 42. Heat is supplied to the liash chamber through heater 44 to vaporize the carbon disulfide solvent and thereby precipitate the soluble sulfur. The soluble sulfur precipitate is removed from the flash chamber 42, ltered, dried and recycled to the melting chamber through a conveying line 46. The vaporous solvent is recovered from the ash chamber through vapor line 48 and condensed to a liquid within condenser 50. The condensed solvent is then recycled to the bottom of the extraction column through pump 52 and solvent return line 54. Make up solvent is added to the solvent stream through line 56 at pump 52.

The insoluble sulfur leaving the extraction column iS filtered and introduced into a vacuum llash chamber 58 through conveying line 60. Heat is supplied to the flash column with heater 62 at a temperature of from 90 to 130 to ash any residual solvent from the particular sulfur. The dry sulfur is recovered and immediately cooled to shipping temperatures of 35 LF. to 80 F.

The solvent flashed in chamber 58 is recovered through vapor line 62 and condensed in condenser 64. The condensed solvent is recycled to the extraction column through return line 66 by pump 68.

The aforegoing process description represents only one embodiment of this invention. Several modifications can be made without changing the essence of the invention and such are considered within the scope of the instant invention.

In a particularly preferred embodiment, the quenched sulfur particles leaving filter 24 are hardened and dried before their introduction into the extraction column 38. I have found that this hardening step improves the ultimate stability of the extracted insoluble sulfur as well as renders the particles more susceptible to grinding, etc. The hardening step is accomplished by maintaining the temperature of the particles between 30 and 90 F. while simultaneously exposing the particles to air for a period of 16 to 48 hours. This period, however, can be reduced by using higher air exposure temperatures. Thus, if temperatures of 11G-140 F. are employed, the hardening period is reduced to 3-6 hours.

The invention is further illustrated by the following examples which are demonstrative of specific modes of practicing the invention and which are not intended as limiting the scope of the invention as defined by the claims.

EXAMPLES 1-3 These examples are presented to demonstrate the effectiveness of the hydrogen peroxide component in stabilizing the insoluble sulfur. In each of the experiments, 1000 grams of sulfur are added to a 1/2 gallon steel heating chamber and slowly heated to 285 IF. The molten sulfur is allowed to gravity drain through a lA-inch diameter tube 2 inches in length, and maintained at 600 by electrical heating tapes which are Wrapped around the tube. The tube discharges the sulfur into a l2-inch diameter cylindrical steel container containing approximately gallons of water. The water contains 1 weight percent of hydrogen peroxide.

The quenched sulfur is recovered from the container by draining off the aqueous solution and the particles allowed to harden in air for 24 hours at ambient conditions. At the end of the hardening period, 1000 grams of the sulfur is ground to approximately 20-100 mesh and contacted with 3 gallons of carbon disulfide in a Soxhlet extractor. Approximately 400 grams of insoluble sulfur is recovered from the extractor after an extraction period of days.

The recovered insoluble sulfur is then tested for its stability in `air at 90 C. In this test, several 1 gram samples of the sulfur are heated to 90 C. for a period of 16 hours. A sample is removed from the test after various times during the stability run and analyzed for its insoluble sulfur content. Table l below, land FIG. 2, demonstrate the' results of this stability test. The ta'ble expresses the amount of insoluble sulfur reverted to the soluble form as percent reversion with la greater percent reversion representing a less stable sulfur product.

The above procedure is repeated except that no hydrogen peroxide is employed in the quenching bath. The stability of the insoluble sulfur produced is similarly tested and the results a-re also presented in Table l and shown in FIG. 2.

The stability of a leading commercial insoluble sulfur product is tested in the same manner as described above, and results from this test are also presented in Table 1 and shown in FIG. 2. The commercially available insoluble sulfur is a representative sample of the insoluble sulfur currently sold on a large scale to the process industries. This sulfur product s referred to hereinafter as commercial brand.

The above table demonstrates that the insoluble sulfur produced from the aqueous hydrogen peroxide bath has superior stability to the insoluble sulfur quenched in water only or the commercial available insoluble sulfur (Crystex).

The accompanying FIG. 2 graphically demonstrates the data of Table 1 and illustrates the percent reversion of the insoluble sulfur products over a 16 hour test period. Curve A represents the insoluble sulfur produced by quenching molten polymeric sulfur in water, curve B represents the commercially available insoluble sulfur and curve C represents the insoluble sulfur obtained by quenching the molten polymeric sulfur in aqueous hydrogen peroxide. The lowest curve (curve C) illustrates that less reversion occurs at C. for any exposure period than the other tested samples.

Although I have illustrated the present invention in connection with specific embodiments thereof, it is not intended that the illustration set forth above shall be regarded as limitations upon the scope of the invention, but rather, it is intended that the invention be defined by the reagents and steps, and their equivalents, set forth in the following claims.

I claim:

1. A process for producing insoluble sulfur which comprises quenching molten polymeric sulfur at a temperature of from 400 to 832 F. in an aqueous solution maintained between about 35 and 90 F. and containing from about 0.1 to l0 Weight percent of hydrogen peroxide.

2. The process defined in claim 1 wherein said molten polymeric sulfur is injected into said aqueous solution through a nozzle capable of producing droplets of said molten polymeric sulfur having a mean diameter of between 0.25 inch and 0.0015 inch.

3. The process defined in claim 1 wherein said molten polymeric sulfur is injected into a reservoir of said aqueous peroxide solution wherein said solution is present in -an amount of 20 to 5000 pounds per pound of sulfur present in said solution.

4. The process defined in claim 1 wherein said molten polymeric sulfur is injected into a reservoir of said aqueous peroxide solution and wherein said reservoir is agitated so as to circulate the solution within the reservoir.

5. The process defined in claim 1 wherein said aqueous solution also contains from 0.001 to l weight percent of a surfactant.

6. The method defined in claim 1 including the steps comprisingzv injecting said molten polymeric sulfur into an agitated reservoir of said aqueous peroxide solution to produce solidified sulfur particles consisting of soluble sulfur and from about 35 to 60 weight percent of insoluble sulfur;

recovering said solidified particles from said aqueous solution;

contacting said recovered particles with a solvent capable of dissolving soluble sulfur for a period sufficient to extract at least 70 percent of said soluble sulfur from said particles; and

yrecovering said extracted particles from said solvent.

7. The method defined in claim 6 wherein the additional step of hardening said recovered particles prior to the contacting with said solvent is performed by exposing the particles to an inert atmosphere at a temperaure of about 30 to 140 F. for a period of from 3 to 48 hours.

8. The method defined in claim 6 wherein said aqueous solution contains from 0.001 to 1 weight percent of a surfactant.

9. The method defined in claim 1 wherein said aqueous solution contains from 0.5 to 5 weight percent of hydrogen peroxide and also contains from 0.001 to l Weight percent of a Water-soluble surfactant and including the steps comprising:

injecting said molten sulfur into an agitated reservoir of from 20 to 5000 pounds of said aqueous peroxide solution per pound of sulfur within said reservoir to produce solidi-fied sulfur particles consisting of soluble sulfur and from about 35 to 60 weight percent of insoluble sulfur;

recovering said solidied particles from said reservoir;

contacting said recovered particles with a Solvent selected from the group consisting of carbon disulfide, ethylene dichloride, methylene dichloride, benzene, toluene and xylene for a period suicient to extract at least 80 percent of said soluble sulfur from said particles; and

recovering said extracted particles from said solvent.

10. The method defined in claim 9 wherein the additional step of hardening said recovered particles prior to the contacting with said solvent is performed by exposing the particles to air at a temperature of about to F. for a period of from 16 o 48 hours.

References Cited UNITED STATES PATENTS NORMAN YUDKOFF, Primary Examiner S. I. EMERY, Assistant Examiner U.S. Cl. X.R. 

